Photoconductivity Of Poly Research Articles

Photoconductivity of Poly(Diphenylene Phthalide) Thin Films Doped with Fullerene Derivatives

The use of polymer dielectrics as a matrix for fullerene derivatives allows photoconductive properties of fullerene-containing materials to be induced. Results are presented from studying the properties of poly(diphenylene phthalide) (PDP) doped with fullerene derivatives.

An in-depth investigation in photoconductivity of Poly(vinyl alcohol)/Starch/Magnetite nanoparticle composite films for optoelectronic applications

This communication demonstrates the potentials of hybridizing (or modifying) poly (vinyl alcohol)/starch composite with magnetite nanoparticle (PVA/St-MNP) to prepare semiconductor and photoconductor polymeric films. The collection of materials composing the newly prepared composite demonstrated satisfactory electrical and photo conductivity and photo sensitivity for optoelectronic applications. The films were prepared with varied contents of magnetite nanoparticles via a solution mixing and casting evaporation method. The structures and morphological surfaces of the films were assessed using FTIR, TGA/DSC, SEM and XRD. The conductivity behavior and light response of the prepared composite films were studied. The current density was also studied for the film samples with different concentrations of MNPs at different applied fields. The current density was found to be dependent on both the field and the MNP content. The results showed a high photo sensitivity of the composite films towards white light. The photo sensitivity of the prepared film samples was found to increase with increasing the MNP content, and reached 14 at 1300 lx for the film containing 12% MNP. The dependence of photoconductivity on light intensity confirmed the existence of traps in the composite films. The life time and differential life time of the pure polymer and composite blends were determined to be within the range 0.67–0.78 and 3.7–457 S. respectively, by studying the transient photoconductivity.

Exceptional photoconductivity of poly(3-hexylthiophene) fibers through in situ encapsulation of molybdenum disulfide quantum dots.

Photo-responsive, electrically conductive nanostructures are highly desirable for wide-ranging applications in energy harvesting, nanophotonic and optoelectronic devices. To this end, we realize self-assembled, photoconductive hybrids of poly(3-hexylthiophene) (P3HT) micro- and nano-fibers integrated with MoS2 quantum dots (QDs). We present an innovative strategy to impregnate QDs within the walls of the P3HT fibers resulting in the emergence of the controllable photoconductivity of the QD-P3HT hybrid. The maximum photoconductivity (>80% higher than pristine P3HT) is observed at 360 nm and originates from a synergistic combination of (a) defect healing and quenching of surface trap states in QDs by P3HT and (b) efficient generation and transfer of photo-excited charges from P3HT to QDs. This mechanism is substantiated by a concomitant decrease in the excited-state lifetime of the QD-P3HT hybrid. Furthermore, a linear correlation between the enhancement in the emission of QDs and the emission quenching of P3HT supports the proposed mechanism of excited-state charge transfer. Finally, the hybrid of MoS2 nanosheets (NS) with P3HT fibers (NS-P3HT) does not exhibit any photo-conductivity and instead exhibits ground state charge transfer, underlying the critical role of quantum confinement effects operating in the QD-P3HT hybrid. Thus, we demonstrate a synergistic, self-assembled QD-P3HT hybrid exhibiting optically controllable electrical conductivity in the solid state as novel functional materials for optoelectronic applications.

Photocurrent enhancement in polythiophene doped with silver nanoparticles

We studied the spectral dependence of the influence of silver nanoparticles (Ag NPs) on the photoconductivity of poly(3-hexylthiophene) (P3HT) thin films. 7±2nm silver nanoparticles were synthesized by thermal decomposition of an organometallic silver salt in organic solvent. Optical properties of the mixture of P3HT and Ag NPs and thin films with various Ag content were investigated. Spectral dependences of the photocurrent were measured for the films cast on the top of interdigitated microelectrodes. Antibatic behavior of the photocurrent with respect to the absorption spectrum was observed. Results shows 40–150 times enhancement of the photocurrents, depending on the wavelength, in films doped with Ag NPs compared with the pristine films. The existing theories on the influence of metallic nanoparticles in the photoactive layer of organic solar cells are reviewed and discussed.

Enhancement of photoconduction in a conjugated polymer through doping with copper nanoparticles

We investigated the effect of doping with copper nanoparticles (Cu NPs) on photoconductivity of poly(3-hexylthiophene) P3HT films. ∼20 nm Cu NPs were fabricated in a simple one step reduction process in hydrophobic environment. Structure, morphology and optical properties of the Cu nanoclusters were characterized. Films of P3HT containing Cu NPs were fabricated and their optical and electrical properties investigated. The results indicate that the change of the efficiency of the light absorption brought about by the effect of plasmonic resonances is minor, but there is a substantial influence of the metal nanoparticles on the efficiency of the photogeneration of charges in P3HT.

Morphology and photoconductivity of poly- N-vinylcarbazole-cellulose triacetate Langmuir–Schaefer films

Cellulose triacetate (CTA) was doped with poly( N-vinylcarbazole) (PVK) via the oxidative polymerization of N-vinylcarbazole with ferric chloride to form polymer blends. Langmuir–Schaefer (LS) films of the polymer blends were fabricated. The morphology of the cellulose triacetate-poly( N-vinylcarbazole) (PC) blends were analyzed using transmission electron microscopy. The pressure–area isotherm of PC blends revealed the possibility of compact monolayer formation at air–water interface. The voltammetric investigation of PC blends showed an appreciable electrochemical behavior. The photoinduced charge transfer across a donor/acceptor hybrid interface provided an effective method to study the photoelectrochemical properties of the PC polymer films.

Spectral distribution of photocurrent in poly(6- tert-butyl-3-methyl-3,4-dihydro-2 H-1,3-benzoxazine)

The spectral distribution of photoconductivity in poly(6- tert-butyl-3-methyl-3,4-dihydro-2 H-1,3-benzoxazine) was studied in the sandwich configuration with indium tin oxide and silver electrodes. The photocurrent was found to originate mainly from the bulk dissociation of excitons with lesser contribution from electrode-mediated exciton dissociation. The molecule was fluorescent, but in the presence of the electron acceptor molecule 2,4,6-trinitrophenol (TNP), the intensity was reduced. The reduction in fluorescence intensity corresponded to an increase in photocurrent. The molecule showed photoconductivity in the visible without any sensitizers, which makes it suitable for stable photorefractive composites.

Spectral sensitization of photoconductivity of poly(N-epoxypropylcarbazole) and benzaldehyde diphenylhydrazones by pyrylium dyes and their heteroanalogues

The sensitizing activity of γ-pyrylocyanines and their heteroanalogues with respect to poly(N-epoxypropylcarbazole) and benzaldehyde diphenylhydrazones was studied. The influence of the dye anion and cation on its sensitizing ability was shown: the change in the sensitizing activity upon introducing a complex metal-containing anion into the dye molecule is due to a change in the donor-acceptor properties of the molecule and redistribution of the probabilities of excited-state deactivation processes. It was found that the maximum sensitization efficiency of pyrylium dyes was attained at the difference of 0.26–0.28 V between the electrochemical oxidation potentials of the sensitizer dye and the organic semiconductor.

Photoconductivity in fullerene-doped polysilane thin films

Flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements have been performed to study the transport properties of charge carriers in the polysilane films. The effect of C 60 concentrations on photoconductivity of poly(methylphenylsilane) (PMPS) and poly( n-hexylphenylsilane) (PHPS) films has been studied using a variety of excitation light sources. The value of ϕ ∑ μ , which is the product of quantum efficiency of photocarrier generation ( ϕ) and sum of moibilities of the carriers ( ∑ μ ), depends strongly on C 60 concentration upon exposure of 532 nm. The quantum efficiency reaches ∼0.06 with C 60 concentration at 5.7 mol%, and saturates at the higher concentrations. The ϕ ∑ μ value increases considerably upon exposure of 193 nm up to 1.22 × 10 −3 cm 2/Vs without significant dependence on C 60 concentration, suggesting the direct formation of electron-hole pair by 6.39 eV photon absorption with the higher ϕ value at ∼0.12. The present technique gave the estimates of intra-chain mobility of charge carriers in PMPS and PHPS, and one-order magnitude higher intra-chain mobility was observed in PHPS than that in PMPS. This is suggestive of a highly ordered Si backbone conformation in PHPS. The intra-chain mobility in PMPS, however, is at least two orders of magnitude higher than the mobility values estimated by conventional time-of-flight techniques. Thus we conclude that the higher mobility than ∼10 −3 cm 2/Vs ( E ∼ 0) is realizable even with PMPS by precise synthesis and device fabrication free from disordering, defects, impurities, etc.

Spectral Sensitization of Photoconductivity of Poly(N-epoxypropylcarbazole) and Benzaldehyde Diphenylhydrazones by Ternary Complexes of Triphenylmethane Dyes

Spectral sensitization of photoconductivity of poly(N-epoxypropylcarbazole) and benzaldehyde diphenylhydrazones by chlorides and ternary complexes of triphenylmethane dyes was studied. It was shown that an increase in the sensitization activity of a triphenylmethane dye upon replacement of chloride anion in its molecule with a complex anion containing metal was due to a change in the electron-acceptor ability of the dye molecule.

PA32 液晶性高分子poly(9,9-dioctylfluorene)の偏光に依存した光伝導特性(物理・物性)

PA32 液晶性高分子poly(9,9-dioctylfluorene)の偏光に依存した光伝導特性(物理・物性)

Second-order process photocurrent in conducting polymer

We have carried out time-resolved measurement for second-order processes of photoconductivity in poly(3-octylthiophene) (PAT8) and poly(3-dodecylthiophene) (PAT12). The external electric field and fullerene (C 60 ) doping effects for the second-order process of photoconductivity have been demonstrated. The external electric field and C 60 doping enable to control the amount of the free charge carriers for the photoconductivity.

Time-Resolved Study of Fullerene Doping Effects on Photoluminescence and Photoconductivity of Poly(3-alkylthiophene)

We have carried out time-resolved measurements of photoluminescence and photocurrent in poly(3-octylthiophene) (PAT8) doped with fullerene (C60). For photocurrent study, we applied a laser two-correlated-pulse technique, which permitted the selection of electronic processes connected with recombination of intermediate short-living species responsible for the formation of free charge carriers. The wavelength and pulse width of the laser pulses were 400 nm and 150 fs, respectively, and delay time (Δt) between correlated pulses was controlled within the ps time domain. It was shown that the average photocurrent in undoped samples has a prominent component originating from interpair recombination of polaron pairs. This component, however, changed with doping: with low doping (C60 less than 0.1 mol%) it increased, but with higher doping (C60 up to 0.5 mol%) it disappeared. It was shown that the electron transfer from π-conjugated segments of PAT8 to C60 takes about 10 ps, and leads to the formation of polaron pairs which dissociate into free charge carriers much faster (lifetime is much shorter than 3 ps) than the pairs formed without doping.

Extrinsic photoconductivity in poly(3-dodecylthiophene) sandwich cells

We have measured the photocurrent action spectra of the Al/poly(3-dodecylthiophene)(P3DDT)/ITO and Au/P3DDT/ITO sandwich cells. The photoinjection from both ITO and Au electrodes was observed at room temperature. No polarity effect was found in the ITO/P3DDT/Au device at low temperatures. The photoinjection from ITO electrode is found not effective at low temperatures. The photocurrent at low temperatures was attributed to photoinjection from Au electrode at both polarity of bias voltage. A phenomenological model of photoconductivity in poly(3-dodecylthiophene) sandwich cells at low-electric fields and low temperatures is proposed. An approach for photoconductivity enhancement in conducting polymers is discussed.

Photoelectrochemical response and photoconductivity of poly(3-methylthiophene)

We report on the photoelectrochemical response and photoconductivity of poly(3-methylthiophene), PMeT, films deposited on different substrates. The frequency dependency of the modulated photoconductivity of PMeT ( ρ=3.6×10 3 Ω cm) is sublinear indicating that the measured photoconductivity is not due to a thermal effect caused by sample heating. An interesting feature was the larger backwall photoconductivity (with the laser beam reaching the film from the substrate side), when compared to photoconductivity in the normal, frontwall illumination. This result is an indication for heterogeneity in the deposited film. The photoelectrochemical response of PMeT films in contact with the electrolyte was studied by spectral response and by the time dependence of the photoelectrochemical response under irradiation with the Ar + laser light (close to the maximum of the spectral photoresponse), with light intensity varying from 10 −5 W cm −2 to 30 mW cm −2. From that experiment we can infer that charge trapping occurs mainly in the polymer surface in contact with the electrolyte. Another experiment was performed with two different light beams, one from a lamp plus monochromator, chopped and at low intensity and another from an Ar + laser, continuous and at high intensity. When the laser beam incides from the electrolyte side, i.e. when light is absorbed in the space-charge layer, we observe a strong drop in the photocurrent. We suppose that the same space-charge layer trapping phenomenon is responsible for the drop in the photocurrent.

Photoconductivity of poly(dimethylsilane) vacuum deposited films in connection with their photoreactivity

Polysilanes are both photoreactive and photoconductive materials owing to their σ-conjugated electrons. We investigate transient behavior of photocurrent under UV irradiation in photomodified poly(dimethylsilane) vacuum deposited films. Slow increase of photocarrier generation accompanied with photoscission of the conjugation is observed, which is significantly enhanced in an oxygen atmosphere. This increase can be explained by accelerated dissociation of excitons, assuming charge transfer to acceptors from metastable Si dangling bonds that are created under the irradiation and disappear upon annealing.

Photoconductivity of poly(2,5-diheptyloxy-p-phenylene vinylene) in the air atmosphere: Magnetic-field effect and mechanism of generation and recombination of charge carriers.

The photoconductivity of poly(2,5-diheptyloxy-p-phenylene vinylene) (HO-PPV) increases upon application of an external magnetic field. This magnetic-field effect (MFE) is significantly enhanced in the presence of the oxygen of air. Two types of MFE are revealed in samples of HO-PPV. The first one is a prompt MFE connected with the existence of coupled pairs of charge carriers, as precursors for photoconductivity: these pairs dissociate thermally and/or in an external electric field, producing mobile carriers. The second MFE is delayed, and is shown to be connected with the reaction of triplet and singlet excitons with ${\mathrm{O}}_{2}$. The reaction changes inertially the concentration of ${\mathrm{O}}_{2}$ molecules dissolved in the bulk of the polymer, its rate being dependent on magnetic field. MFE allowed us to clarify the mechanism of photogeneration of HO-PPV: Positive mobile charge carriers responsible for the photocurrent are produced in the dissociation of primary singlet excitons by oxygen, photo-oxidation products, and other weak dopants like ${\mathrm{C}}_{60}$ molecules. The probability of charge-carrier generation in the reaction with ${\mathrm{O}}_{2}$ molecules is found to be higher than with ${\mathrm{C}}_{60}$ clusters. An enhancement of the photoconductivity of samples in air is connected with that factor and also with a significant increase of the lifetime of charge carriers before recombination. Recombination of positive charge carriers with oxygen negative ions is very slow, giving quasipersistent photoconductivity of the polymer in air. \textcopyright{} 1996 The American Physical Society.

Photoconductivity of poly(methylphenyl silylene) doped with dinitrobenzenes

Abstract Poly(methylphenyl silylene) PMPSi was doped with the following compounds of the electron acceptor type: p-dinitrobenzene (pDNB), m-dinitrobenzene (mDNB), and o-dinitrobenzene (oDNB), up to concentrations of 3mol%. The quantum yield of charge carrier generation φ(cc) is significantly increased, relative to that of neat PMPSi, by pDNB (about four times at a field F = 2 × 107 V m−1 and 3mol%. mDNB and oDNB exert only a small effect on φ(cc). The extent of increase in φ(cc) is correlated with the electron affinity EA; both of them increase in the order oDNB 0 interact (probably electrostatically) with holes passing through the polymer matrix. This results in an increase in the activation energy of μ or, in terms of the hopping transport model, in a broadening of the distri...

Photoconductivity in poly(biphenylmethyl silylene)

Quantum yields of charge carrier formation, ϕ; (cc), in poly(biphenylmethyl silylene), PBMSi, and poly(methylphenyl silylene), PMPSi, have been determined at 23 °C with the aid of the xerographic discharge method. At F = 1 × 108 V/m and λinc = 330–360 nm: ϕ (cc) = 0.10 (PBMSi) and ϕ (cc) = 0.03 (PMPSi). Upon the addition of 2,3,5,6-tetrachlorobenzoquinone (chloranil) at c = 3 mol%, to the polysilylene films, the quantum yields were increased: ϕ (cc) = 0.21 (PBMSi) and ϕ (cc) = 0.13 (PMPSi). The mobility of charge carriers μ in PBMSi is about one order of magnitude lower than in PMPSi. Upon addition of 3 mol% chloranil to PBMSi μ increased slightly.

Photoconductivity in C 60 doped polyacetylene derivative

Photoconductivity in poly(o-trimethylsilylphenylacetylene) (PTMsiPA) is enhanced intensively by small amount of C 60 doping at three wavelength ranges corresponding to (a) forbidden transition (1.8eV) between h u and t 1u states of C 60, (b) inter-band transition (>2eV) in PTMSiPA and (c) allowed transition (3.5eV) between h u and t 1g levels of C 60. Remarkable polarity effect of applied voltage is observed in the photoconduction spectra in C 60 doped PTMSiPA due to uniform carrier excitation in range (a) and non-uniform carrier excitation in range (b) and (c), proving that positively charged carriers (S + solitons) are mainly contributing to photoconductivity. These results are discussed in terms of photo-induced charge transfer between PTMSiPA and C 60, taking into account the role of photoexcited polarons and charges solitons S + in polymeric chains.